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A 15-year-old boy was evaluated for a 3-month history of sharp pain in the upper left chest. Notable findings on the physical examination included a low-frequency long systolic ejection murmur in the left infraclavicular region. The results of a 15-lead ECG were normal (Figure 1). A complete transthoracic echocardiogram was performed and the result was reported as normal (Figure 2). Because of the unusual character of the murmur, the referring cardiologist sent the patient for cardiac magnetic resonance imaging.

Figure 2. Parasternal short-axis echocardiogram with color demonstrates the LPA arising from the right and coursing leftward.

A complete cardiac magnetic resonance study was performed that included gadolinium-contrasted images. On axial and 3D reconstruction gadolinium-enhanced images, the left pulmonary artery (LPA) was seen arising from the superior aspect of the right pulmonary artery (RPA) (Figures 3 and 4⇓). The LPA was mildly compressed and coursed posterior to the trachea at the level of the carina. No significant compression of the main stem, right, or left bronchi were present (Figures 5 and 6⇓). Pulmonary blood flow imaging showed mild preferential flow to the right lung, with 69% to the right lung and 31% to the left lung (Figures 7 and 8⇓). Pulmonary arterial velocity mapping demonstrated laminar flow to the RPA (Figure 9) and increased velocity and narrowing of the LPA (Figure 10).

Figure 5. T1-weighted cross-sectional axial magnetic resonance imaging demonstrates the LPA arising from the right and coursing posterior to the bronchus. The LPA is narrowed at the origin and midpoint from the impression of the right and left bronchi.

Figure 10. Velocity mapping imaging of the LPA demonstrates an increased signal intensity in the superior portion of the LPA, suggesting increased velocity and narrowing.

Anomalous origin of the LPA from the RPA is a rare congenital anomaly first described on autopsy by Glaevecke and Doehle in 1897.1 The term vascular sling was first used to describe the condition by Contro et al2 in 1958 to distinguish it from a vascular ring. In pulmonary artery slings, the LPA typically arises anomalously from the posterior aspect of the RPA, passes over the right mainstem bronchus near its origin, and courses leftward between the trachea and esophagus to the left pulmonary hilum.

Until recently, no evidence of a genetic link to the presence of pulmonary artery slings has been documented. Mowat-Wilson syndrome is a multiple congenital anomaly/mental retardation syndrome associated with pulmonary artery sling.3,4 Haploinsufficiency of a gene termed ZFHX1B (also known as SIP1) on chromosome 2 is responsible for this condition, and clinical genetic testing for Mowat-Wilson syndrome recently became available.3

The embryology of the pulmonary artery sling has not been completely delineated. Varying theories as to the possible developmental origins exist. Although some authors have proposed that the pulmonary artery sling possibly represents failure of LPA development with a resultant branch forming from the RPA to the left hilum,5 the explanation by Sade et al6 seems the most complete and probable. In that description, a pulmonary artery sling arises when there is caudal capillary connection of the left post-branchial plexus with the RPA, resulting in the LPA coursing posterior to the tracheobronchial tree.

The prevalence of pulmonary artery sling is purely conjectural, as there is no way to know the true number of asymptomatic cases that exist. In the known cases, pulmonary artery sling has been shown to have a male to female ratio of 3:2. The vast majority of patients have symptoms (90%), and of those, 90% present the first year of life.7 Asymptomatic pulmonary artery slings are typically diagnosed incidentally in adolescence or adulthood.8 Respiratory symptoms are most common and are usually characterized by wheezing and stridor with a prolonged expiratory phase. Associated anomalies of the tracheobronchial tree frequently (51%) include either abnormal branching, abnormal distribution of cartilage in the walls of the trachea and major bronchi including complete cartilaginous rings, or intrinsic stenosis.7 Tracheobronchial tree obstruction is absent in adults diagnosed with pulmonary artery sling, though it can be associated with dysphagia.8 Major cardiovascular anomalies are present in up to 30% of patients with a pulmonary artery sling.7

The prognosis of pulmonary artery sling is variable depending on presentation. Surgery is the standard of care for all symptomatic patients, as medically managed patients have a death rate of 90%.9 Spontaneous improvement in symptomatic patients occurs, though uncommonly.8 Surgical morbidity and mortality rates in symptomatic patients have improved markedly since the first successful repair by Willis Potts in 1953.10 Recently, Fiore et al11 have demonstrated a 79% survival rate in patients undergoing correction via transection of the LPA and reimplantation anterior to the trachea, as advocated by Backer et al.12 In contrast to symptomatic patients, the prognosis for asymptomatic patients is excellent, and surgical intervention is not indicated.

Disclosures

Dr Fogel has been a consultant for and received honoraria from Siemens. The remaining authors report no conflicts.